The ZIII Gundam is a new special purpose MS design by Anaheim Electronics based on the design of the ZZ Gundam, ZII and S Gundam. The design was completed quite a while ago but never used because general purpose mobile suits were more popular after the S Gundam generation.
After 0092, the EFF had to prepare for war with Neo-Zeon and began the development of the Nu Gundam for use by Captain Amuro Rey. The ZIII served as a design that led to the development of the Nu Gundam. The unusual characteristics of the Zeta system as a TMS are applied to the ZIII.
When the development project was restarted, Anaheim Electronics did not use the basic frame structure of the first design, but instead a original style created by a new design chief. No expense was spared in its development: bio-sensors, generator, thrusters, armor, all are top of the line. Overall the specs are very high compared to other MS of the era. Much of the design and technology cultivated in the S-Gundam is adopted into the ZIII’s options and parts.
Of noteworthy mention is the equipping of the "I-Shield." The I-Shield spreads Minovsky particles packed together along the armor surface, which can deflect beam weaponry. Minovsky particles have mass, when a beam hits the body, the spread particles repulse the beam back to it’s incoming direction. In this way it acts as a sort of "Reactive Armor". The shield forms instantaneously at the time it is needed but requires enormous amounts of electrical energy. The ZIII also has 2 I-Field generator units mounted on the shoulders with a dedicated sub-generator to power them.
NOTE: "Zeissa" seems to be a Japanese pronunciation of a shortening of "Zeta Third."